Treatment of Cancer with Enzalutamide and a CYP3A4 Inhibitor

ABSTRACT

This disclosure provides a dosage regimen for co-administration of enzalutamide and a strong CYP3A4 inducer in the treatment of cancer.

This application claims priority to and incorporates by reference U.S. provisional application Ser. No. 62/204,281, filed on Aug. 12, 2015, and U.S. provisional application Ser. No. 62/204,954 filed on Aug. 13, 2015.

Each reference cited in this disclosure is incorporated herein in its entirety.

TECHNICAL FIELD

This disclosure relates generally to cancer treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the effects of rifampin (as well as other drugs and intrinsic/extrinsic factors) on the pharmacokinetic parameters C_(max) and AUC_(0-inf) for enzalutamide and its major active metabolite N-desmethyl enzalutamide.

FIGS. 2A-B. Graphs showing mean plasma enzalutamide concentrations after a single dose of 160 mg enzalutamide alone or in the presence of multiple doses of 600 mg rifampin once daily. The vertical line at 336 h signifies the end of rifampin treatment. FIG. 2A, linear. FIG. 2B, semi-log scale plot.

FIGS. 3A-B, Graphs showing mean plasma M1 concentrations after a single dose of 160 mg enzalutamide alone or in the presence of multiple doses of 600 mg rifampin once daily. The vertical line at 336 h signifies the end of rifampin treatment. FIG. 3A, linear. FIG. 3B, semi-log scale plot.

FIGS. 4A-B. Graphs showing mean plasma M2 concentrations after a single dose of 160 mg enzalutamide alone or in the presence of multiple doses of 600 mg rifampin once daily. The vertical line at 336 h signifies the end of rifampin treatment. FIG. 4A, linear. FIG. 4B, semi-log scale plot.

FIGS. 5A-B. Graphs showing mean plasma sum of enzalutamide plus M2 concentrations after a single dose of 160 mg enzalutamide alone or in the presence of multiple doses of 600 mg rifampin once daily. The vertical line at 336 h signifies the end of rifampin treatment. FIG. 5A, linear. FIG. 5B, semi-log scale plot.

FIG. 6. Graph showing mean plasma concentration-time curve of rifampin on day 8 after multiple doses of 600 mg rifampin once daily.

FIG. 7. Graph showing mean and individual C_(2h) plasma concentrations of rifampin during multiple doses of 600 mg rifampin once daily for 21 days.

DETAILED DESCRIPTION

Enzalutamide, 4-{3-[4-cyano-3-(trifluoromethyl)phenyl]-5,5-dimethyl-4-oxo-2-sulfanylideneimidazolidin-1-yl}-2-fluoro-N-methylbenzamide (e.g., XTANDI®), is an androgen receptor inhibitor and can be used to treat cancers such as prostate cancers, breast cancers, and ovarian cancers. Enzalutamide is also a strong CYP3A4 inducer in humans; at steady state, enzalutamide reduces the plasma exposure to the CYP3A4 substrate midazolam. There are, however, situations in which co-administration of enzalutamide with a strong CYP3A4 inducer (e.g., carbamazepine, phenobarbital, phenytoin, rifabutin, rifampin, rifapentine) are nevertheless desirable or cannot be avoided. In a drug-drug interaction trial in healthy volunteers, a single 160 mg oral dose of XTANDI® was administered alone or after multiple oral doses of rifampin (strong CYP3A4 and moderate CYP2C8 inducer). Rifampin decreased the AUC_(0-inf) of enzalutamide and its major active metabolite N-destnethyl enzalutamide by 37% with no effect on C_(max). The results are summarized in FIG. 1. Thus, in which co-administration of enzalutamide with a strong CYP3A4 inducer (e.g., carbamazepine, phenobarbital, phenytoin, rifabutin, rifampin, rifapentine) are desirable or cannot be avoided, the daily dose of enzalutamide may be increased from, e.g., 160 mg/day to 200-300 mg/day (e.g., 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300 mg/day).

“Co-administration ” of enzalutamide and a strong CYP3A4 inhibitor means administration in any manner in which the pharmacological effects of enzalutamide and the strong CYP3A4 inhibitor overlap in the patient at the same time. Co-administration does not require that both agents be administered in a single pharmaceutical composition, in the same dosage form, by the same route of administration, or for the same length of time.

Enzalutamide is typically formulated for oral administration. Formulations of enzalutamide are disclosed, e.g., in the prescribing information for XTANDI®, and in US 2014/0378517, US 2014/0179749, and US 2014/0100256.

Patients who can be treated with the disclosed co-administration regimes include patients with prostate cancer (including metastatic prostate cancer, castration-resistant prostate cancer, hormone-sensitive prostate cancer, metastatic castration-resistant prostate cancer, metastatic hormone-sensitive prostate cancer), breast cancer (including triple-negative breast cancer), and ovarian cancer. Prostate cancer patients who can be treated using the disclosed co-administration regimes include patients with metastatic castration-resistant prostate cancer (CRPC) who had previously received chemotherapy (e.g., docetaxel) as well as patients with CRPC who are chemotherapy-naïve.

The following example illustrates but does not limit the scope of the appended claims.

EXAMPLE 1 Pharmacokinetics

Data handling. The actual sampling time of enzalutamide and its metabolites for 6 subjects (7 samples in total), and the actual sampling time of the 2-hour rifampin sample of subject 10002 on Day 21 deviated more than 10% (of the scheduled time point. Therefore, the concentrations from these samples were excluded from the summary statistics, but were included in the calculation of the pharmacokinetic parameters.

Enzalutamide and its Metabolites M1 (Inactive) and M2 (Active)

Mean enzalutamide plasma concentrations versus time profiles (linear and semi-logarithmic) are presented in FIG. 2. Summary statistics of enzalutamide pharmacokinetic parameters are shown in Table 1. In Table 2., the statistical assessments of the effect of rifampin on enzalutamide after a single dose of enzalutamide are presented.

As indicated in the semi-logarithmic concentrations versus time profiles, elimination of enzalutamide was faster in the presence of rifampin compared to after administration of enzalutamide alone. For all subjects in the rifampin treatment arm, the last quantifiable enzalutamide concentration was measured prior to the end of the rifampin dosing period (up to 13 days after enzalutamide dosing). Therefore, it was deemed appropriate to calculate AUC_(inf), t_(1/2), CL/F and V_(z)/F using non-compartmental methods. % AUC was low and individual values ranged between 0.658% and 4.56%.

In the presence of rifampin, enzalutamide AUC_(0-336hr) and AUC_(inf) were 63% (geometric mean ratio [GMR]:36.79; 90% CI: 33.36-40.57) and 66% (GMR: 33.76 (90% CI: 30.31-37.60) lower, respectively, compared to enzalutamide alone. C_(max) was not significantly changed (GMR: 93.03; 90% CI: 83.67-103.45), and similar mean tam values were observed (i.e., 1.039 hours versus 1.078 hours), with the comparable ranges of individual values.

Mean t_(1/2) was shorter when enzalutamide was given in the in the presence of rifampin (30.70 h) compared to enzalutamide alone (90.10 hours). Mean apparent clearance was higher in the presence of rifampin (1.856 L/h) compared to enzalutamide alone (0.6330 L/h), while the apparent volume of distribution (V_(z)/F) did not change.

Between subject variation in enzalutamide AUC_(0-336hr), AUC_(inf) and C_(max) was low and was not influenced by the presence of rifampin, with values ranging between 13.2% and 1.9.4%.

TABLE 1 Summary Statistics of Plasma Enzalutamide Pharmacokinetic Parameters After Single Dose Administration of 160 mg Enzalutamide Alone or in the Presence of Multiple Doses of 600 mg Rifampin Once Daily Parameter n Mean SD (CV %) Min Median Max Enzalutamide AUC_(0-336 h) (μg · h/mL) 14 239.2 41.06 (17.2) 179 233.0 320 AUC_(0-t) (μg · h/mL) 14 257.7 50.35 (19.5) 187 253.7 336 AUC_(inf) (μg · h/mL) 14 262.0 50.91 (19.4) 191 259.0 341 C_(max) (μg/mL) 14 4.931 0.8196 (16.6) 3.10 5.140 5.94 t_(max) (h) 14 1.078 0.4804 (NA) 0.500 0.9100 2.00 t_(1/2) (h) 14 90.10 27.25 (30.2) 35.5 85.69 142 CL/F (L/h) 14 0.6330 0.1259 (19.9) 0.470 0.6184 0.840 V_(z)/F (L) 14 79.82 21.68 (27.2) 41.1 78.11 123 Enzalutamide + Rifampin (Test) AUC_(0-336 h) (μg · h/mL) 14 87.50 11.55 (13.2) 71.8 84.80 109 AUC_(0-t) (μg · h/mL) 14 85.41 10.99 (12.9) 69.3 82.67 105 AUC_(inf) (μg · h/mL) 14 87.58 11.68 (13.3) 72.0 84.75 110 C_(max) (μg/mL) 14 4.567 0.6435 (14.1) 3.20 4.560 5.70 t_(max) (h) 14 1.039 0.3497 (NA) 0.500 1.000 2.00 t_(1/2) (h) 14 30.70 6.162 (20.1) 17.7 31.80 39.4 CL/F (L/h) 14 1.856 0.2350 (12.7) 1.46 1.888 2.22 V_(z)/F (L) 14 81.59 17.45 (21.4) 52.0 80.49 119 CV %: coefficient of variation expressed as percentage; Max: maximum; Min: minimum; NA: not applicable

TABLE 2 Statistical Assessment of the Effect of Multiple Doses of Rifampin on Exposure Parameters of Plasma Enzalutamide After Single Dose Administration of 160 mg Enzalutamide Geometric LS Means Enzalutamide Enzalutamide + Ratio (%) Parameter (Units) (Reference) Rifampin (Test) (Test/Reference) 90% CI (%) n 14 14 AUC_(0-336 h) (μg · h/mL) 236.0 86.82 36.79 33.36-40.57 AUC_(inf) (μg · h/mL) 257.4 86.89 33.76 30.31-37.60 C_(max) (μg/mL) 4.862 4.523 93.03  83.67-103.45 LS: Least squares

Enzalulamide Metabolite M1

Mean M1 plasma concentrations versus time profiles (linear and semi-logarithmic) are presented in FIG. 3. Summary statistics of M1 pharmacokinetic parameters are shown in Table 3. In Table 4, the statistical results of the effect of rifatnpin on M1 after a single dose of enzalutamide are presented.

Based on the mean concentration-time profiles, the maximum MI plasma concentrations were comparable between treatments; however, the maximum plasma concentration was reached somewhat earlier in the presence of rifampin. Elimination of M1 was faster in the presence of rifampin, though the elimination of M1 did not change after discontinuation of rifampin at t=336 hours.

In the presence of rifampin, M1 AUC_(0-336hr) and AUC_(inf) were 15% (GMR: 84,94; 90% CI: 69.07-104.46) and 32% (GMR: 67.53; 90% CI: 44.56-102.33) lower, respectively compared to enzalutamide alone. The 90% CI of the GMRs for both parameters were wide. It should be noted that AUC_(inf) could only be accurately determined for 4 subjects in the enzalutamide treatment arm (treatment arm 1) and 6 subjects in the enzalutamide+rifampin treatment arm (treatment arm 2). For AUC_(inf) values for which the percentage extrapolated (% AUC) were higher than 20%, the AUC_(inf) was excluded from the statistical analysis. Mean M1 t_(1/2) was somewhat shorter in the presence of rifampin (194.5 hours) compared to enzalutamide alone (223.9 hours).

C_(max) appeared to be similar (GMR:96.56; 90% CI: 77.68-120.02); however, median t_(max) was reached earlier in the presence of rifampin (58.21 hours) compared to after administration of enzalutamide alone (109.6 hours), with smaller ranges of individual values in the presence of rifampin.

M1 MPRs, molecular weight corrected and based on AUC_(inf), were higher in the presence of rifampin compared to enzalutamide alone, with mean values of 0.4897 (range: 0.210 to 0.809) and 0.2165 (range: 0.152 to 0.314), respectively.

Between subject variation in M1 AUC_(0-336hr), AUC_(inf) and C_(max) was moderate and was not influenced by the presence of rifampin, with values ranging between 27.5% and 47.3%.

TABLE 3 Summary Statistics of Plasma M1 Pharmacokinetic Parameters After Single Dose Administration of 160 mg Enzalutamide Alone or in the Presence of Multiple Doses of 600 mg Rifampin Once Daily Parameter n Mean SD (CV %) Min Median Max Enzalutamide AUC_(0-336 h) (μg · h/mL) 14 32.49 8.930 (27.5) 20.3 31.38 54.5 AUC_(0-t) (μg · h/mL) 14 47.87 16.73 (35.0) 25.9 46.66 92.4 AUC_(inf) (μg · h/mL) 8 62.14 19.84 (31.9) 38.2 57.39 102 C_(max) (μg/mL) 14 0.1414 0.04662 (33.0) 0.0761 0.1350 0.238 t_(max) (h) 14 109.6 74.5 (NA) 36.0 119.1 263 t_(1/2) (h) 12 223.9 62.85 (28.1) 86.2 236.6 303 MPR (MWC) 12 0.2233 0.05737 (25.7) 0.157 0.2194 0.323 Enzalutamide + Rifampin (Test) AUC_(0-336 h) (μg · h/mL) 14 28.35 9.840 (34.7) 13.0 27.54 47.8 AUC_(0-t) (μg · h/mL) 14 34.33 13.76 (40.1) 13.0 34.59 64.5 AUC_(inf) (μg · h/mL) 4 44.09 20.87 (47.3) 22.3 42.40 69.3 C_(max) (μg/mL) 14 0.1374 0.04751 (34.6) 0.0724 0.1370 0.230 t_(max) (h) 14 58.21 32.19 (NA) 12.0 47.92 120 t_(1/2) (h) 10 194.5 53.56 (27.5) 131 183.2 274 MPR (MWC) 10 0.4894 0.2085 (42.6) 0.217 0.4757 0.844 CV %: coefficient of variation expressed as percentage; Max: maximum; Min: minimum; MPR (MWC): metabolite versus parent ratio (molecular weight corrected); NA: not applicable

TABLE 4 Statistical Assessment of the Effect of Multiple Doses of Rifampin on Exposure Parameters of Plasma M1 After Single Dose Administration of 160 mg Enzalutamide Enzalutamide Enzalutamide + (Reference) Rifampin (Test) Geometric Geometric Ratio (%) Parameter (Units) n LS Mean n LS Mean (Test/Reference) 90% CI (%) AUC_(0-336 h) (μg · h/mL) 14 31.43 14 26.70 84.94 69.07-104.46 AUC_(inf) (μg · h/mL) 8 59.62 4 40.26 67.53 44.56-102.33 C_(max) (μg/mL) 14 0.1346 14 0.1300 96.56 77.68-120.02 LS: Least Squares

Enzalutamide Metabolite M2

Mean M2. plasma concentrations versus time profiles (linear and semi-logarithmic) are presented in FIG. 4. Summary statistics of M2 pharmacokinetic parameters are shown in Table 5. In Table 6, the statistical results of the effect of rifampin on M2 after a single dose of enzalutamide are presented.

Based on the mean concentration-time profiles, maximum M2 plasma concentrations were higher and were reached earlier in the presence of rifampin compared to enzalutamide alone. Elimination of M2 was slightly faster in the presence of rifampin. The elimination of M2 did not change after discontinuation of rifampin at t=336 hours.

In the presence of rifampin, M2 AUC_(0-336h), was 15% higher (GMR: 114.8; 90% CI: 103.49-127.34), while AUC_(inf) was 15% lower (GMR: 84.74 (90% CI: 77.13-93.11) compared to enzalutamide alone. % AUC was low and ranged between 1.25% and 5.79%. Mean M2 t_(1/2) was somewhat shorter in the presence of rifampin (154.7 hours) compared to enzalutamide alone (190.4 h). M2 C_(max) was 34% higher (GMR: 133.7; 90% CI: 118.63-150.76), and median t_(max) was reached earlier (i.e., 71.86 hours versus 167.7 hours).

M2 MPR, molecular weight corrected and based on AUC_(inf), was higher in the presence of rifampin compared to enzalutamide alone, with mean values of 3.443 (range: 2.71 to 4.33) and 1.385 (range: 1.04 to 2.08), respectively.

Between subject variation in M2 AUC_(0-336hr), AUC_(inf) and C_(max) was low and was not influenced by the presence of rifampin, with values ranging between 11.0% and 20.8%.

TABLE 5 Summary Statistics of Plasma M2 Pharmacokinetic Parameters After Single Dose Administration of 160 mg Enzalutamide Alone or in the Presence of Multiple Doses of 600 mg Rifampin Once Daily Parameter n Mean SD (CV %) Min Median Max Enzalutamide AUC_(0-336 h) (μg · h/mL) 14 197.6 41.15 (20.8) 146 184.1 286 AUC_(0-t) (μg · h/mL) 14 344.3 58.19 (16.9) 249 338.3 440 AUC_(inf) (μg · h/mL) 14 354.0 59.18 (16.7) 255 351.0 451 C_(max) (μg/mL) 14 0.7546 0.1778 (23.6) 0.542 0.7145 1.18 t_(max) (h) 14 161.3 37.00 (NA) 120 167.7 265 t_(1/2) (h) 14 190.4 31.07 (16.3) 142 182.3 253 MPR (MWC) 14 1.431 0.3156 (22.1) 1.07 1.373 2.15 Enzalutamide + Rifampin (Test) AUC_(0-336 h) (μg · h/mL) 14 224.0 24.72 (11.0) 173 221.9 263 AUC_(0-t) (μg · h/mL) 14 292.1 33.51 (11.5) 221 293.5 338 AUC_(inf) (μg · h/mL) 14 297.9 33.52 (11.3) 226 299.4 343 C_(max) (μg/mL) 14 0.9949 0.1413 (14.2) 0.743 1.010 1.29 t_(max) (h) 14 66.75 19.23 (NA) 47.9 71.86 120 t_(1/2) (h) 14 154.7 18.58 (12.0) 125 152.5 190 MPR (MWC) 14 3.558 0.5368 (15.1) 2.81 3.372 4.47 CV %: coefficient of variation expressed as percentage; Max: maximum; Min: minimum; MPR (MWC): metabolite versus parent ratio (molecular weight corrected); NA: not applicable

TABLE 6 Statistical Assessment of the Effect of Multiple Doses of Rifampin on Exposure Parameters of Plasma M2 After Single Dose Administration of 160 mg Enzalutamide Geometric LS Means Enzalutamide Enzalutamide + Ratio (%) Parameter (Units) (Reference) Rifampin (Test) (Test/Reference) 90% CI (%) n 14 14 AUC_(0-336 h) (μg · h/mL) 194.0 222.7 114.8 103.49-127.34 AUC_(inf) (μg · h/mL) 349.3 296.0 84.74 77.13-93.11 C_(max) (μg/mL) 0.7370 0.9856 133.7 118.63-150.76 LS: Least Squares

Sum of Enzalutamide Plus M2

Mean sum of enzalutamide plus M2 plasma concentrations versus time profiles (linear and semi-logarithmic) are presented in FIG. 5. Summary statistics of the sum of enzalutamide plus M2 pharmacokinetic parameters are shown in Table 7. In Table 8, the statistical results of the effect of rifampin on the sum of enzalutamide plus M2 after a single dose of enzalutamide are presented.

Based on the mean concentration-time profiles, mean sum of enzalutamide plus M2 plasma concentrations were comparable between treatments up to roughly 48 hours after administration. Thereafter, plasma concentrations of the sum of enzalutamide plus M2 declined slightly faster in the presence of rifampin. After discontinuation of rifampin at t=336 hours, no change in decline was observed.

In the presence of rifampin, sum of enzalutamide plus M2 AUC_(0-336hr) and AUC_(inf) were 28% (GMR: 71.56; 90% CI: 66.39-77.13) and 37% (GMR 63.26; 90% CI: 58.17-68.79) lower, respectively, compared to enzalutamide alone. Mean tv, was somewhat shorter in the presence of rifampin (149.4 hours) compared to enzalutamide alone (178.6 hours)

C_(max) was comparable between treatments (CMR.: 94.32; 90% CI: 85.05-104.60), and similar mean t_(max) values were observed (i.e., 1.039 hours versus 1.078 hours) with the same ranges of individual values. Between subject variation in sum of enzalutamide plus M2 AUC_(0-336hr), AUC_(inf) and C_(max) was low and was not influenced by presence of rifampin, with values ranging between 9.7% and 16.4%.

TABLE 7 Summary Statistics of Plasma Sum of Enzalutamide plus M2 Pharmacokinetic Parameters After Single Dose Administration of 160 mg Enzalutamide Alone or in the Presence of Multiple Doses of 600 mg Rifampin Once Daily Parameter n Mean SD (CV %) Min Median Max Enzalutamide AUC_(0-336 h) (μg · h/mL) 14 436.9 59.33 (13.6) 359 421.1 574 AUC_(0-t) (μg · h/mL) 14 603.5 90.32 (15.0) 466 604.9 774 AUC_(inf) (μg · h/mL) 14 612.5 92.00 (15.0) 472 614.5 779 C_(max) (μg/mL) 14 4.980 0.8153 (16.4) 3.36 5.192 5.97 t_(max) (h) 14 1.078 0.4804 (NA) 0.500 0.9100 2.00 t_(1/2) (h) 14 178.6 29.04 (16.3) 128 168.3 221 Enzalutamide + Rifampin (Test) AUC_(0-336 h) (μg · h/mL) 14 311.5 30.34 (9.7) 256 311.9 371 AUC_(0-t) (μg · h/mL) 14 379.6 38.40 (10.1) 304 384.9 445 AUC_(inf) (μg · h/mL) 14 385.2 38.38 (10.0) 309 390.8 450 C_(max) (μg/mL) 14 4.674 0.6340 (13.6) 3.33 4.665 5.80 t_(max) (h) 14 1.039 0.3497 (NA) 0.500 1.000 2.00 t_(1/2) (h) 14 149.4 17.79 (11.9) 119 148.5 179 CV %: coefficient of variation expressed as percentage; Max: maximum; Min: minimum; NA: not applicable

TABLE 8 Statistical Assessment of the Effect of Multiple Doses of Rifampin on Exposure Parameters of Plasma Sum of Enzalutamide plus M2 After Single Dose Administration of 160 mg Enzalutamide Geometric LS Means Enzalutamide Enzalutamide + Ratio (%) Parameter (Units) (Reference) Rifampin (Test) (Test/Reference) 90% CI (%) n 14 14 AUC_(0-336 h) (μg · h/mL) 433.3 310.1 71.56 66.39-77.13 AUC_(inf) (μg · h/mL) 606.0 383.3 63.26 58.17-68.79 C_(max) (μg/mL) 4.911 4.633 94.32  85.05-104.60 LS: Least Squares

Rifampin

Mean rifampin plasma concentrations versus time profile during 1 dosing interval on day 8 is presented in FIG. 6. In FIG. 7, individual and mean rifampin C2h plasma concentrations that were obtained during the entire dosing period of 21 days are presented. Summary statistics of rifampin pharmacokinetic parameters are shown in Table 9.

Mean plasma rifampin concentrations on day 8 were in line with reported concentrations (Martin et al, 2011; Polk et al, 2001) indicating that relevant concentrations for CYP3A4 and CYP2C8 induction were likely reached by day 8. Median t_(max) was reached 2 hours post-dose. C_(2h) concentrations were generally consistent throughout the 21-day dosing period indicating that steady-state rifampin exposure was achieved prior to and maintained after administration of enzalutamide.

Intersubject variation in rifampin C_(2h) was low with values ranging between 12.0% and 22.6%

TABLE 9 Summary Statistics of Rifampin Pharmacokinetic Parameters After Multiple Doses of 600 mg Rifampin Once Daily Day 8 Parameter n Mean SD (CV %) Min-Max Median C_(min) (μg/mL) 14 0  NA (NA) 0-0 NA C_(2 h) (μg/mL) 14 6.759 0.9330 (13.8)  5.24-8.27 6.625 C_(max) (μg/mL) 14 7.163 1.222 (17.1) 5.24-8.89 7.035 t_(max) (h) 14 1.720 0.4700 (NA)  1.00-2.00 2.000 AUC_(tau) 14 35.59 4.450 (12.5) 28.3-46.4 35.25 CV %: coefficient of variation expressed as percentage; Max: maximum; Min: minimum; NA: not applicable

Conclusion

After administration of a 160 mg single enzalutamide dose in the presence of multiple doses of 600 mg rifampin once daily:

Enzalutamide AUC_(inf) was 66% lower (GMR 33,76; 90% CI: 30.31-37.60) compared to enzalutamide alone, while C_(max) was comparable (GMR: 93.03; 90% CI: 83.67-103.45).

Mean t_(max) values were similar (i.e., 1.039 hours versus 1.078 hours with comparable ranges of individual values.

M1 AUC_(0-336hr) and AUC_(inf) were 15% (GMR: 84.94; 90% CI: 69.07-104.46) and 32% (GMR: 67.53; 90% CI: 44.56-102.33) lower, respectively, while appeared to he similar (GMR: 96.56; 90% CI: 77.68-120.02) however, median M1 t_(max) was reached earlier (i.e., 58.21 hours versus 109.6 hours).

M2 AUC_(inf) was 15% lower (GMR: 84.74; 90% CI: 77.13-93.10, while M2 C_(max) was 34% higher (GMR: 133.7; 90% CI: 118.63-150.76). Median M2 t_(max) was reached earlier (i.e., 71.86 hours versus 167.7 hours).

Sum of enzalutamide plus M2 AUC_(inf) was 37% lower (GMR 63.26; 90% CI: 58.17-68.79), while was similar (GMR: 94.32; 90% CI: 85.05-104.60). Mean t_(max) values were similar 1.039 hours versus 1.078 hours), with comparable ranges of individual values.

Rifampin C_(2h) concentrations indicated that steady-state rifampin exposure was achieved prior to and maintained after administration of enzalutamide on day 8.

EXAMPLE 2 Pharmacodynamics

Datahandling. For subject 10037 and subject 10046 in the enzalutamide treatment arm (treatment arm 1), the actual time of urine sampling on day 1 was not within 180 minutes inclusive of enzalutamide dosing and/or pre-dose of rifampin. In addition, for many subjects, urine samples taken post enzalutamide dose were not taken within 180 minutes of the ‘virtual’ enzalutamide dosing time (i.e., day 1 enzalutamide dosing time [enzalutamide treatment arm {treatment arm 1}] and day 8 enzalutamide dosing time [enzalutamide+rifampin treatment arm {treatment arm 2}]) and/or pre-dose of rifampin. The 6β-hydroxycortisol and cortisol concentrations of these urine samples and obtained 6β-hydroxycortisol/cortisol ratios were excluded from summary statistics.

6β-Hydroxycortisol/Cortisol Ratio for Treatment Arm 1

In treatment arm 1 (enzalutamide alone), the urinary 6β-hydroxycortisol/cortisol ratio increased from a baseline mean value of 6.8±5.1 on day Ito a maximum value of 8.3±3.6 on day 15, returning to baseline (i.e., 6.2±1.9) on day 22.

6β-Hydroxycortisol/Cortisol Ratio for Treatment Arm 2

In treatment arm 2 (enzalutamide in combination with rifampin), the urinary 6β-hydroxycortisollcortisol ratio increased from a baseline mean value of 6.9±4.2 on day 1 to 24.2±22.1 on day 8 (the day of enzalutamide administration), From day 8 to day 22 (the end of rifampin administration), mean ratios were variable and ranged between 19.12. and 29.38, returning to baseline(i.e., 6.4±3.2) by day 36.

TABLE 10 Summary Statistics of Urine 6β-hydroxycortisol/Cortisol Ratio After a Single Dose of 160 mg Enzalutamide Alone or in the Presence of Multiple Doses of 600 mg Rifampin Once Daily Enzalutamide Day n Mean SD CV % Min Max Median 1 11 6.844 5.060 73.9 1.74 17.3 5.256 4 11 5.760 1.840 32.0 2.51 8.11 6.390 8 9 7.855 3.232 41.1 3.83 14.5 8.094 15 11 8.347 3.637 43.6 4.28 14.8 6.872 22 9 6.204 1.892 30.5 3.71 9.31 5.647 29 8 6.519 2.785 42.7 3.15 11.5 6.590 36 8 8.212 5.261 64.1 2.00 19.6 7.153 43 8 6.576 3.062 46.6 3.13 13.1 6.294 50 7 5.119 2.094 40.9 2.15 7.59 4.802 Enzalutamide + Rifampin n Mean SD CV % Min Max Median 1 14 6.855 4.238 61.8 2.73 17.7 5.730 4 14 19.25 14.43 75.0 6.94 65.8 14.44 8 14 24.23 22.12 91.3 9.16 92.2 15.98 11 14 23.04 13.19 57.3 11.2 56.2 16.82 15 14 19.12 8.586 44.9 8.28 41.7 17.95 22 14 29.38 16.64 56.6 7.26 56.4 23.42 29 12 13.01 11.77 90.5 4.98 47.8 9.727 36 11 6.356 3.164 49.8 4.14 15.0 5.410 43 10 6.216 2.581 41.5 2.58 9.86 6.486 50 10 7.067 2.724 38.5 3.31 10.9 6.894 57 12 6.974 2.235 32.0 2.84 10.0 7.018 CV %: coefficient of variation expressed as percentage; Max: maximum; Min: minimum

Conclusion

The pharmacodynamic assessment confirmed that rifampin had produced an inductive effect on CYP3A4 by the time that enzalutamide was administered on day 8; whereas, a single dose of enzalutamide alone produced a minimal inductive effect on CYP3A4. 

1. A method of treating cancer, comprising co-administration to a patient in need thereof a therapeutically effective dose of enzalutamide and a CYP3A4 inducer, wherein the therapeutically effective dose of enzalutamide is 200-300 mg per day.
 2. The method of claim 1, wherein the cancer is selected from the group consisting of prostate cancer, breast cancer, and ovarian cancer.
 3. The method of claim 1, wherein the therapeutically effective dose of enzalutamide is 240 mg per day.
 4. A method of treating metastatic castration-resistant prostate cancer, comprising co-administration to a patient in need thereof (i) 240 mg/day of enzalutamide and (ii) a CYP3A4 inducer.
 5. The method of claim 1, wherein the CYP3A4 inducer is selected from the group consisting of carbamazepine, phenobarbital, phenytoin, rifabutin, rifampin, and rifapentine.
 6. The method of claim 4, wherein the CYP3A4 inducer is selected from the group consisting of carbamazepine, phenobarbital, phenytoin, rifabutin, rifampin, and rifapentine. 